The present invention relates to an in-line roller skate, which comprises a frame connected to a shoe or a plurality of frame portions which can be attached to this shoe, wherein at least three running rollers are disposed one behind the other in the running direction on the frame or the frame portions and said running rollers comprise along their periphery in each case a rolling surface which extends in a curved manner in an axial cross-section and which is formed in each case substantially symmetrical with respect to the longitudinal middle plane of the running rollers, wherein the rolling surfaces of at least one front running roller and at least one rear running roller with respect to an axis-parallel tangential plane to the rolling surface comprise at a spaced disposition from the longitudinal middle plane a: comparatively greater perpendicular spacing than the. rolling surface at least of a middle running roller, so that when the roller skate tilts sidewards with respect to the tangential plane the front and/or rear running roller are raised from a contact surface or the contact pressure of these running rollers on the contact surface is reduced.
The present invention also relates to a set of running rollers.
In-line roller skates are already known and are commercially available in a large number of different designs. The running rollers of known roller skates are disposed one behind the other in a horizontal plane and generally comprise a rolling surface which is parabolic in the axial cross-section, wherein all running rollers of a roller skate are substantially identical.
In contrast thereto U.S. Pat. No. 5,207,454 A (Blankenburg) describes a roller skate wherein a single running roller is provided in the middle between the front and rear end of the frame and provided in front of and behind this running roller in each case are two ball rollers which are mounted by way of a ball bearing in a shell-shaped recess in the frame. In contrast to the roller skates mentioned in the introduction the running roller comprises a rectangular- cross-section. The ball rollers can move in any direction so that the roller skater can negotiate particularly narrow curves. This known roller skate is, however, encumbered by poor characteristics with respect to the straight travel, which poor characteristic is naturally undesired.
Furthermore, in the known DE 39 186 17 A (K. K. Gakushu Kenkyuscha) an exemplified embodiment of a roller skate is described (FIG. 3), wherein two middle running rollers are wider than in each case two front and rear running rollers. When viewed from the side, the total of six running rollers are disposed along a concave curve. The rolling surface of all six running rollers is designed in the form of a cylindrical peripheral surface and therefore does not comprise any convex curvature. The two wider middle rollers are to ensure that the roller skate runs in a more stable manner since when traveling in a straight line only these two rollers contact the ground. However, this feature is also inadequate for achieving stable travel in a straight line since in this case only two adjacent rollers of the six rollers contact the ground.
One problem which still needs to be overcome when developing in-line roller skates relates to the improvement of the inefficient manner in which such roller skates negotiate curves.
It is known in this connection to provide running rollers with a steerable suspension or to provide a so-called inner-steering for the running wheels in the region of the rotational axis. Although such structural features render it possible to achieve good steering behaviour, they are complicated and expensive.
A further known feature for improving the manner in which in-line roller skates negotiate curves resides in the fact that the foremost and rearmost wheels are disposed slightly higher than the middle wheels, wherein, however, the disadvantage of less efficient travel in a straight line must be accepted. For other in-line roller skates available on the market it is possible to adjust the distance to the ground in such a manner that in one case all running rollers lie on the same height or that in an other case there is adjusted a so-called xe2x80x9crockeringxe2x80x9d position with the front and/or rear running rollers higher than the middle running rollers.
Commercially available roller skates comprise a rolling surface with a continuous convex profile in the cross-section. Various published documents, e.g. U.S. Pat. No. 698,110 A (Foy), DE 11 100 60 C (Steiger) or GB 908,566 (Lambert) do, however, also disclose other profile shapes, e.g. combinations of convex and concave profile portions which merge into each other by way of a turning point or a transitional edge. Each roller skate does, however, comprise two identical rollers. Furthermore, DE-PS 827 913 (Maassen) describes a roller skate having two running wheels, wherein two wheels having a rolling surface which is circular in cross-section can be replaced by two wheels having a rolling surface which is rectangular in cross-section.
U.S. Pat. No. 2,570,349 A (Kardhordo, according to FR 959 408 A) discloses a roller skate having one single main roller and two or more auxiliary rollers. In this document it is stated, that in curve racing the main roller and one or more auxiliary rollers contact the race course simultaneously, and it is clear, that depending if there is a forward or a backward lean, it is the front or the rear roller which contacts the course surface. However, essential problems are associated with this skating technique in practice. Changing from one roller to two rollers unavoidably causes a tilting movement forward and backward respectively, and furthermorexe2x80x94because of the widely differing rolling surfaces of the rollers contacting the groundxe2x80x94the direction of motion changes in different ways, unexpected for the skater, depending if the front auxiliary roller or the rear auxiliary roller contacts the ground. The center of gravity of the skater will be always either in front of or behind the main roller resulting in the fact that a stable position cannot be reached at any time. Since the rolling surfaces of all rollers merge discontinuous into the lateral surface forming a sharp edge a sudden and dangerous change in road behaviour takes place starting from a certain angular position of the roller skates.
An object of the invention is therefore to improve the manner in which in-line roller skates negotiate curves by means of convenient and inexpensive features without having an adverse effect on the travel in a straight line, e.g. by xe2x80x9crockeringxe2x80x9d, and to provide a set of running rollers for such in-line roller skates. Furthermore a highly tilted position of the roller skate should be possible without sudden changes in road behaviour.
For solving the problem the invention provides an in-line roller skate as mentioned in the beginning, which is characterized in that provided in the middle portion of the roller skate are two middle running rollers which are disposed immediately one behind the other and whose rolling surfaces are identical, wherein these rolling surfaces comprise in the transition region to the lateral surfaces of the running rollers in each case a rounded running shoulder which in the event of a sidewards tilting of the roller skate contacts the contact surface.
By virtue of this feature when travelling in a straight line generally all running rollers are in contact with the substrate, whereas when the roller skate is tilted sidewards the front and rear running roller is raised from the substrate or at least their contact pressure is reduced and thus it is possible to negotiate the curve in a more convenient manner.
In one advantageous embodiment of the invention it is provided that the running shoulder of the rolling surface of a middle running roller comprises a comparatively greater curvature than the remaining central section of the rolling surface of the same running roller. This results in good running properties when negotiating curves. The curvature of the central section of the rolling surface may be zero.
To further facilitate negotiating of curves it is possible that the rolling surface of the at least one front and at least one rear running roller is comparatively narrower in width at a spaced position from its contact surface than the rolling surface of the at least one middle running roller. This renders it possible in an advantageous manner to use identical bearing parts for all types of rollers, because the wheel bodies of the front and the rear rollers may have the same thickness in the region of their axes.
Another solution to the object of the invention may be reached by a set of rollers consisting of one front and one rear roller and two middle rollers having the features as mentioned above.